Ziegler-Natta (ZN) polyolefin catalysts are well known in the field of polymers. Generally, they comprise (a) at least a catalyst component formed from a transition metal compound of Group 4 to 6 of the Periodic Table (IUPAC, Nomenclature of Inorganic Chemistry, 1989), a metal compound of Group 1 to 3 of the Periodic Table (IUPAC), and, optionally, a compound of group 13 of the Periodic Table (IUPAC) and/or an internal donor compound. ZN catalyst may also comprise (b) further catalyst component(s), such as a cocatalyst and/or an external donor.
Various methods have been developed for preparing ZN catalysts. In one method the catalyst components are impregnated on a particulate support material, such as silica, to obtain a solid ZN catalyst system. For example in WO 01 55230 of Borealis a solution of a chlorine-containing compound, e.g. ethylaluminium dichloride, and a magnesium hydrocarbyloxy compound is first prepared and the obtained solution is impregnated together with a transition metal compound into a porous particulate support.
Solid ZN catalysts, wherein no external support, such as silica, is used, are also known in the field. U.S. Pat. No. 4,496,660 of Dow discloses a catalyst support formed by reacting in an inert diluent (A) the reaction product of (1) an organomagnesium component, (2) an oxygen- and/or nitrogen-containing compound, optionally dissolved or dispersed to a halide containing compound of a transition metal; and (B) a transition metal-free halide source. In the examples the compound (1) is combined with the compound (2) and a halogen-free aluminium compound and then a transition metal compound is added. The obtained solids are then reacted with the compound (B). EP 591 922 of Mitsui discloses a titanium catalyst prepared by contacting (A) a solution of a halogen-containing magnesium compound, an alcohol having at least 6 carbon atoms and a hydrocarbon solvent, with an organoaluminum compound to form a solid complex which is treated with (B) a tetravalent titanium compound.
WO 99 55741 of Fina describes a process for preparing a Ziegler-Natta catalyst by (i) mixing in a hydrocarbon solvent a dialkyl magnesium compound with a chlorinating agent to precipitate a magnesium dichloride derivative. The chlorinating agent is obtainable from the reaction between an alcohol ROH and an alkyl aluminium chloride. The precipitate is washed or reacted to remove unwanted reducing species and the obtained magnesium dichloride derivative is titanated. WO 99 58584 of Borealis describes a further method for preparing a ZN catalyst, wherein a Mg compound is first reacted with an alcohol and the obtained complex is added to a solution of chlorine containing aluminium compound to form a solid reaction product. The obtained slurry is used as such in the next step and to this slurry titanium tetrachloride is added. EP 197 166 of Dow describes a catalyst solution, wherein (A) an organomagnesium compound, (B) an organic OH-containing compound, (C) a reducing halide source of Al or B and (D) a transition metal compound are added in the order (A), (B), (C) and (D); or (A), (B), (D) and (C), and the obtained reaction solution is used as such for the polymerisation.
Accordingly, although much development work has been done in the field of Ziegler-Natta catalysts, there remains a continuing search for alternative or improved methods of producing ZN catalysts with desirable properties.
In addition, it is desired to obtain catalysts resulting in different and/or specific properties of olefin polymers, e.g. desired molecular weight distribution, and, if copolymers are to be prepared, improved co-monomer distribution and co-monomer sensitivity, and even more to have a better control of the balance in lamella thickness and crystallinity of copolymers.
Further, morphology of the solid catalyst is a feature, which affects on the polymer morphology, and thus this feature is to be considered, as well. If solid, supported catalysts are prepared, the external catalyst support, such as silica, has to be selected carefully in order to achieve good morphology for the catalyst. Further, it is known in the art to use as catalyst support Mg dichloride complexes, which are titanated in order to get a final catalyst. By selecting a proper way to prepare such a Mg-complex carrier having desired morphology many desired properties can be achieved. This kind of support preparation method is disclosed in WO 04 055068. An essential step in this preparation process is the washing step of the solid support in order to remove undesired soluble material from the solid support. A disadvantage of this process is that the removed soluble effluent contains valuable catalyst components, which are handled as waste material.